Abstract
3.2 Materials and methods
3.2.1 Selection of genotypes used in the evaluation trials
Twenty-nine genotypes were used in both yield and disease evaluation trials. These came from three different sources (Table 3.1). Fifteen cultivars came from ICRISAT, Kenya, varying in their resistance to Fusarium wilt disease. Three local accessions (that were apparently resistant to wilt), originated from the Legume Breeding Section of the Department of Research in the Ministry of Agriculture and Food Security in Malawi (Source: Late H.N. Soko, Chitedze Research Station). The remainder were local landraces of unknown reaction to F. wilt. These landraces included ten that were selected by farmers and traders during the participatory variety selection (Chapter 2).
The two released varieties in Malawi served as controls for wilt resistance, yield and yield components. KAT60/8 and ICEAP00068 were susceptible controls for Fusarium wilt.
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Table 3.1: Pigeonpea genotypes used in evaluation trials Item
No.
Genotype Source Resistance status
to Fusarium wilt
Maturity duration
1 AP1 Malawi local landrace Unknown Unknown
Malawi local landrace Unknown Unknown
2 AP2
Malawi local landrace Unknown Unknown
3 AP3
Malawi local landrace Unknown Unknown
4 AP4
Malawi local landrace Unknown Unknown
5 AP5
Malawi local landrace Unknown Unknown
6 AP6
Malawi local landrace Unknown Unknown
7 AP7
Malawi local landrace Unknown Unknown
8 AP8
Malawi local landrace Unknown Unknown
9 AP9
Malawi local landrace Unknown Unknown 10 AP10
11 ACC2253 Government (Mw) Tolerant Late maturing Tolerant Late maturing 12 ACC2291 Government (Mw)
Tolerant Late maturing 13 ACC2298 Government (Mw)
Late maturing 14 ICP9145 ICRISAT Kenya Resistant (check) in
Malawi, susceptible in Kenya
Late maturing 15 ICEAP00040 ICRISAT Kenya Resistant (check)
16 ICEAP00068 ICRISAT Kenya Susceptible (check) Medium maturing 17 KAT60/8 ICRISAT Kenya Susceptible (check) Early maturing
18 ICEAP00020 ICRISAT Kenya Relatively resistant Late maturing 19 AP19 Malawi local landrace Unknown Unknown
Medium maturing 20 ICEAP00554 ICRISAT Kenya Resistant
Medium maturing 21 ICEAP00540 ICRISAT Kenya Resistant
Medium maturing 22 ICPL87051 ICRISAT Kenya Resistant
23 AP23 Malawi local landrace Unknown Unknown
24 ICEAP00557 ICRISAT Kenya Unknown Medium maturing Late maturing
25 ICEAP00053 ICRISAT Kenya Relatively resistant
Late maturing 26 ICEAP00932 ICRISAT Kenya Relatively resistant
Late maturing 27 ICEAP00933 ICRISAT Kenya Relatively resistant
Late maturing 28 ICEAP00936 ICRISAT Kenya Relatively resistant
29 AP29 Malawi local landrace Unknown Unknown
3.2.2 Evaluations of yield and plant descriptors of local landraces and ICRISAT cultivars
The yield evaluation trial, comprising 29 genotypes, was conducted at Kandiya Research Station in the central region of Malawi (Figure 3.1), about 10 km from Chitedze Research Station. Kandiya Research Station is 1108 masl, 13.973790S, and 033.73085 E. The site 0 is devoid of Fusarium wilt disease. The trial was laid out in a randomised complete block design (RCBD). Each plot comprised two rows (ridges) of 3.3 m long, spaced at 0.9 m apart. The pigeonpea plants were spaced at 300 mm within the row. The trial was planted with the onset of the first rains and no fertilizers were applied to simulate
farmers’ practices. The plot was constantly scouted for insect pests, and Rogor (Dimethoate) at 6.5g / 10 litres water or Acephate (Orthene) at 38ml / 10 litres water was sprayed when the need arose. Weeds were controlled by hand. The trial was repeated over three seasons, 2004/05, 2005/06 and 2006/07. There was drought in the first season and the distribution of the rain was poor, especially towards the end of the season. In the second season, the rainfall was less than in the first season but the distribution was better towards the end of the season than in the first season (Figure 3.2). The trial at Bvumbwe Research Station in 2004/05 was converted from a disease- to a yield-evaluation trial in the first year due to low Fusarium wilt disease pressure.
a b
Figure 3.1: Pigeonpea yield trial at Kandiya Research Station, Lilongwe, Malawi: a) Trial establishment at 3 wk; b) Vegetative growth at 4 mo.
0 50 100 150 200 250 300 350 400 450
October November
December January
February March
April May
Months
Rainfall (mm) mo-1
0 200 400 600 800 1000 1200
Cumulative rainfall (mm)
2004/05 2005/06 2006/07 2004/05 2005/06 2006/07
Figure 3.2: Distribution of rainfall during the season at Kandiya Research Station, Lilongwe, Malawi from 2004 to 2007 (Note: Lines are cumulative while bars are monthly rainfall)
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Data collection in these trials included days to 50% flowering, number of primary, secondary and tertiary branches, plant height at maturity, stem diameter, number of seeds pod-1, yield and 100-seed mass. Observations were also made on flower colour, pod colour, stem colour, pattern of flower streaks, and growth habit (Remanandan, 1990;
ICRISAT, 2006).
3.2.3 Screening of pigeonpea local landraces and ICRISAT cultivars for Fusarium wilt resistance through natural inoculation
Screening of pigeonpea genotypes for their resistances to Fusarium wilt was done over two seasons (2004/05 and 2005/06) at Bunda College and Bvumbwe Research Station sick plots (Figure 3.3). The 29 genotypes were planted in an RCBD. Each plot consisted of two rows of 3.3 m long spaced at 0.9 m apart with pigeonpea plants spaced at 300 mm within the row. The trial was planted with the first rains and hand weeding was done whenever weeds appeared. Chemicals and fertilizers were not applied to pigeonpea to simulate farmers’ conditions and for fear of affecting the impact of the pathogen.
a b
Figure 3.3. Fusarium wilt disease screening trial in the sick plot: a) Trial establishment, b) Infection and damage by Fusarium wilt disease
Data collection in these trials concentrated on the number of pigeonpea plants dying, wilting, or showing typical symptoms of Fusarium wilt as described by Reddy et al.
(1990). Data collection commenced one week after germination, starting with plot stand and later counting the number of diseased and dead plants in each plot. Genotypes with less than 20% wilt, based on stand count plot-1, were considered resistant to the disease. The disease assessment was based on the following scale by Nene and Kannaiyan, (1982):
0 - 20% infection – resistant;
21 - 40% infection – moderately resistant/tolerant;
41 - 60% infection - susceptible;
61 - 80% infection – moderately susceptible;
81 - 100% highly susceptible
3.2.4 Data analysis
The data on both yield and yield components, and diseased/dead plants were analyzed, using analysis of variance (ANOVA) of the Genstat statistical package. Data transformations were done where coefficients of variations were high. Log base e (Loge
(x + c) was used in data transformation, and the value of c was arbitrarily taken as 10.
Fmax (Fujino, 1979) was used to calculate the homogeneity of the data across sites and over seasons. Fmax = S2max / S2min. Accept Ho (homogeneity of data) if Fmax < Fα (k, n – 1).
Only homogenous data were combined in the analysis over sites and/or seasons.
Correlations were also done between Fusarium wilt incidences and other characteristics such as yield, days to 50% flowering, plant height, stem thickness, seed pod-1 and 100- seed mass.